The AgeX trial was set up to test whether cancers could be usefully picked up, without undue harm, in those aged 47 to 49 and those aged 71 to 73.
Photograph: Rui Vieira/PA

Up to 450,000 women in England were not called for their last mammogram before they turned 70 because of a computer failure that goes back to 2009, health secretary Jeremy Hunt has told the House of Commons. He said some women will have avoidably died as a result. Not everybody agrees with him.

Up to 80,000 of these women were enrolled in AgeX, a major NHS trial designed to find out whether extra screening would protect older women from breast cancer. When the trial began in 2009, the records of the women taking part had a “flag” on the NHS system, which meant they did not receive any more routine invitations for screening. Half of those taking part in the trial would have been screened as part of the trial, but the other half would not, enabling researchers to work out whether screening beyond the age of 70 actually saves lives or not.

Hunt told the House of Commons it has taken 10 years for the mistake to be recognised. Some cancers that could have been picked up early and treated will have been missed, he said. As many as 207 women may have died unnecessarily, a tragedy for the women and their families.

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Women are called for breast screening in the UK every three years between the ages of 50 and 70. Not all choose to go, in the light of global findings from researchers that the x-ray screening, called a mammogram, can pick up very small cancers and benign growths that will never cause the woman harm – especially in older people. Last year had the lowest breast screening uptake ever in England, at 71%. In some areas, it was even lower – the lowest was 55.4%.

But at the same time there has been pressure from breast screening advocates and patient groups to extend it to both younger and older women. The AgeX trial was set up in 2009 to test whether cancers could be usefully picked up, without undue harm, in those aged 47 to 49 and those aged 71 to 73.

Across England, 65 breast cancer units recruited women in these two age groups. A computer program selected at random half of the extra women to be screened and half not to be screened.

All the women in the older group, aged 71 to 73, should have had a last routine scan three years after their last mammogram and before their 70th birthday. But the NHS screening computer program appears to have cancelled it. That will have meant that some women entering the trial had their final screening aged 67 or 68. Half the participants were randomly assigned to extra screening. It is the 80,000 in the other arm, the control group, who were first identified as having had their final screening cancelled. It then emerged that this had happened not just to women in the AgeX trial but across the NHS breast screening programme, affecting an estimated 450,000 women, according to Public Health England.

Hunt spoke of a disaster and apologised to women, but although he and the breast cancer charities talked in apocalyptic terms, not everybody shared that interpretation of what had happened. Since January, Public Health England has been investigating and talking to experts, some of whom say it is not as clear cut as Hunt made it appear.

Sir Richard Peto, professor of medical statistics at Oxford University where the AgeX study is run, said what has not been understood is that the screening system works on a three-year cycle. That means some women have their last mammogram at 67, some at 68, some at 69 and some at 70. That’s how the screening system was set up. They have never been offered a last screening specifically in the year of their 70th birthday.

“That automatically means there is going to be a three-year variation. It is misleading to describe this as a disaster,” he told the Guardian.

The randomised trials in AgeX have not yet been concluded, so there is no good evidence as yet even as to the benefits of screening women over 70.

“There is substantial uncertainty as to whether screening is appropriate for older women because although it will pick up some cancers, it will also lead to quite a lot of unnecessary surgical treatment and worry,” said Peto.

The age of last screening is also somewhat random. There is little difference in risk - as far as anyone knows - between the age of 67 and the age of 70 or 71.

The health secretary also acknowledged several times in his statement to the House of Commons that there is no consensus among experts as to whether the benefits of screening for older women outweigh the harms.

But there may still be women whose cancers could have been caught at an early stage and dealt with before they could do serious harm, who have died instead. An inquiry chaired by Lynda Thomas, the chief executive of Macmillan Cancer Support, and Prof Martin Gore from the Royal Marsden cancer hospital will look into each case to find out whether a system that was supposed to help women, actually let some of them down and led to avoidable deaths.

This article was amended on 6 May 2018 to clarify details of the problem in the NHS breast screening programme.